Method of and apparatus for resetting a wire electrode in an operating setup on an electroerosion machine

ABSTRACT

An improved method and apparatus for automatically resetting a wire electrode in an operating setup on an electroerosion (e.g. EDM) machine is disclosed. Upon termination of a given machining operation commenced with a starting hole in the workpiece, the wire electrode spanning in a continuous stretch between a supply side and a collection side is broken in a region adjacent to the workpiece and at one of the opposite sides thereof by forming the wire electrode in the region with at least two coplanar grooves substantially symmetrical about the axis thereof and then applying tension to the wire electrode to break the latter in the region. The broken wire electrode is threaded its broken end into and through a new starting hole preformed in a workpiece for machining a contour therein in a subsequent machining operation to reestablish the continuous stretch of the wire electrode between the supply and collection sides. An air jet may be applied at least in the region of the wire electrode to be heated, grooved and broken to blow off residue of the machining liquid which may remain adherent on the wire electrode to allow the latter to be uniformly heated without any localized thermal stress. This also allows the wire electrode which is broken to form a straight broken end.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation of Ser. No. 261,269 filed May6, 1981, now U.S. Pat. No. 4,513,191.

FIELD OF THE INVENTION

The present invention relates generally to traveling-wire electroerosionprocesses and, more particularly, to an improved method of and apparatusfor automatically resetting a wire electrode in an operating setup on anelectroerosion machine.

The term "electroerosion" used herein is intended to refer broadly to aprocess of electrical machining in general, including an electricaldischarge machining (EDM) process, electrochemical machining (ECM)process and electrochemical-discharge machining (ECDM) process.

The term "wire electrode" used herein is intended primarily to refer toan elongated electrode in the form of a thin continuous wire, but mayinclude any other similar elongate form of the electroerosion electrodesuch as a tape.

BACKGROUND OF THE INVENTION

In traveling-wire electroerosion precesses, a continuous wire electrodeis axially transported by a wire axial drive means from a supply meansto a collection means. In the path of wire travel, a pair of machiningguide members are commonly disposed at opposite sides of an electricallyconductive workpiece to span the traveling wire electrodestraightforwards thereacross traversing the workpiece, thus positioningthe wire electrode in a precise machining relationship with theworkpiece. The electroerosion machine includes a power supply forpassing an electrical machining current, typically or preferably in theform of a succession of electrical pulses, between the wire electrodeand the workpiece across a machining gap flooded with a machiningliquid, e.g. water or an aqueous solution, to electroerosively removematerial from the workpiece. As the material removal proceeds, theworkpiece is displaced transversely relative to the axis of the wireelectrode along a prescribed feed path under the command, preferably, ofa numerical controller, so that a desired contour of cut is generated inthe workpiece.

Wire electroerosion machines are very often required to machine a numberof contours in a workpiece or similar workpieces in a sequence ofoperations. In each operation, it is necessary that machining shouldstart with a hole preformed at a given point associated with eachcontour desired. Thus, prior to proceeding with any given machiningoperation, the wire electrode must be threaded or set through a startinghole and, subsequent to accomplishment of such machining operation, thewire electrode must be removed from the machined contour or the hole andagain threaded or reset through another starting hole associated withanother contour desired in the same or another workpiece. Each resettingoperation needed after a given machining operation before anothertherefore requires breaking, at a region immediately above or below theworkpiece, the wire electrode extending continuously between the supplyand collection sides, repositioning relatively the axis of the wireelectrode and the worktable carrying the workpiece or workpieces,threading the wire electrode from the cut end through the starting holeassociated with the new contour to be machined and then reloading thethreaded wire electrode in the wire axial drive or transpotation meansdownstream of the guide member to establish its continuous axial travelfrom the supply side to the collection site.

In order to eliminate the necessity of the operator's manualintervention, an automatic wire resetting arrangement has advantageouslybeen provided which is designed to execute the foregoing wire resettingoperation automatically. In the known setup, the continuous wireelectrode is broken by cutting with a blade and, prior to cutting, maybe heated and thereby hardened to achieve a desired degree ofstraightness of the cut end thereof. In the conventional arrangement, ananvil is disposed in contact with the wire electrode, the knife bladedisposed on the opposite side of the anvil with respect to the wireelectrode is moved towards the anvil to make a groove on the wireelectrode urged against the anvil and then the clamping means isoperated to apply tension to break the wire electrode at the site of thegroove. Experience has now shown that this arrangement often results ina failure in threading the broken wire electrode through the startinghole which most desirably is as small as possible upon repositioning ofthe machine setup. The failure of threading destroys the automaticresetting function and entails much and unexpected manual interventionby the operator to allow resumption of operation.

It has now been found that a source of conventional difficulty in thewire threading on the traveling-wire electroerosion machine lies in theconfiguration of grooving which has hitherto been applied in the wireelectrode to be broken and reset. Thus, as shown in FIG. 3(a) in theaccompanying drawing, the knife blade in the conventional arrangementhas been operated to make a single groove go in the wire electrode Efrom one lateral side thereof. When the wire electrode E grooved in thismanner is stretched and broken, each end portion of the broken wiretends to bend, as shown in FIG. 3 (b), due to different elongations atone side grooved and the other side not grooved. Because of the thinnessof the wire electrode, a considerable degree of bending thus tends todevelop.

It has been found that another source of the threading difficulty isattributable to a residue of the machining liquid that locally remainsadherent on the wire electrode subsequent to the previous machiningoperation. When the wire electrode portion prior to breaking is heatedfor hardening, a stress tends to develop in the wire due to irregularityin the temperature rise between an area on which the liquid remains inan greater amount and another area on which the liquid remains in alesser amount or does not practically adhere, the stress giving risehere again to a bending of the wire when broken.

OBJECTS OF THE INVENTION

It is, accordingly, an object of the present invention to provide animproved method of automatically resetting a wire electrode in anoperating setup on a traveling-wire electroerosion machine whereby thewire electrode is threaded without fail and thus reset accurately andreliably to allow the subsequent machining operation to be commencedautomatically.

Another object of the invention is to provide an automatic wireresetting apparatus in a traveling-wire electroerosion machine, which isrelatively simple and inexpensive and yet allows a reliable andfail-safe threading and resetting operation on a full automatic basiswithout the operator's intervention.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided, in a firstaspect thereof, a method of automatically resetting a wire electrode inan operating setup on an electroerosion machine, which method comprises:(a) terminating a previous machining operation by shutting off thesupply of a machining electric current to the wire electrode and haltinga machining axial advance of the wire electrode extending in acontinuous stretch from a supply side to a collection side along astraight path formed through a workpiece; (b) breaking the wireelectrode in a region adjacent to the workpiece and located at one ofthe opposite sides thereof by forming the wire electrode in the regionwith at least two coplanar grooves located substantially symmetricalabout the center axis thereof and thereafter applying a tension to thewire electrode to allow the latter to be broken at the grooves; and (c)threading the broken wire electrode from one broken end portion thereofthrough a starting hole preformed in a workpiece for machining a contourtherein in the subsequent machining operation to reestablish thecontinuous stretch of the wire electrode between the supply side and thecollection side thereof.

Prior to step (b) and subsequent to step (a), the method preferablyincludes the step of heating at least a portion of the wire electrodestretched continuously from the supply side to the collection side atleast along the aforementioned region to achieve a hardening thereof.

Preferably, step (a) of the method further comprises halting the supplyof a machining liquid to the wire electrode and the method furthercomprises, prior to step (b), the step of blowing off a residue of themachining liquid that remains adherent on the wire electrode.

The invention also provides, in a second aspect thereof, an apparatusfor automatically resetting a wire electrode in an operating setup on anelectroerosion machine including an electroerosion power supply forapplying a machining electric current to the wire electrode, wire drivemeans for axially advancing the wire electrode extending in a continuousstretch from a supply side to a collection side and liquid supply meansfor furnishing a machining liquid to the wire electrode and a machininggap formed thereby with a workpiece, the apparatus comprising: (a)switch means associated with the power supply and the wire drive meansfor shutting off the supply of the machining electric current to thewire electrode and halting a machining axial advance of the wireelectrode in the continuous stretch, thereby terminating a previousmachining operation commenced with a given starting hole; (b) wirebreaking means comprising (b1) grooving cutter means having at least twoblade means disposed in a region adjacent to the workpiece and at one ofthe opposite sides thereof for forming the wire electrode in the regionwith at least two coplanar cut grooves substantially symmetrical aboutthe center axis thereof and (b2) tension means for applying a tension tothe wire electrode to break the latter at the grooves; and (c) means forthreading the wire electrode from one broken end portions thereofthrough a new starting hole preformed in a workpiece for machining acontour therein in the subsequent machining operation to reestablish thecontinuous stretch of the wire electrode between the supply side and thecollection side.

The apparatus preferably further comprises means for heating, prior tobreaking, the wire electrode for hardening thereof.

The apparatus also preferably includes further means for blowing off aresidue of the machining liquid which remains adherent on at least aportion of the wire electrode to be heated by the heating means.

In accordance with another important feature of the present invention,there is provided in a first aspect thereof a method of automaticallyresetting a wire electrode in an operating setup on an electroerosionmachine, which method comprises: (a) terminating a previous machiningoperation by shutting off the supply of a machining electrical currentto the wire electrode, halting a machining axial advance of the wireelectrode extending in a continuous stretch between a supply side and acollection side along a straight path formed through a workpiece andhalting the supply of a machining liquid to the wire electrode; (b)blowing off a residue of the machining liquid which remains adherent onthe wire electrode at least in a region adjacent to the workpiece and atone of the opposite sides thereof; (c) heating the wire electrode atleast in the said region; (d) breaking, by cutting, the heated wireelectrode at the said region; and (e) threading the broken wireelectrode from one broken end portion thereof through a starting holepreformed in a workpiece for machining a contour therein in thesubsequent machining operation to reestablish the continuous stretch ofthe wire electrode between the supply and collection sides.

The invention also provides in a second aspect according to this featurethereof an apparatus for automatically resetting a wire electrode in anoperating setup on an electroerosion machine including an electroerosionpower supply for applying a machining electric current to the wireelectrode, wire drive means for axially advancing the wire electrodeextending from a supply side to a collection side in a continuousstretch along a straight path formed through a workpiece and liquidsupply means for furnishing a machining liquid to the wire electrode anda machining gap formed thereby with the workpiece, the apparatuscomprising: (a) switch means associated with the power supply, the wiredrive means and the liquid supply means for shutting off the supply ofthe machining electric current to the wire electrode, halting amachining axial advance of the wire electrode and halting the supply ofthe machining liquid to the wire electrode, thereby terminating aprevious machining operation; (b) gas jet means for applying ahigh-pressure stream of a gaseous fluid to the wire electrode in atleast a region adjacent to the workpiece and located at one of theopposite sides thereof to blow off a residue of the machining liquidwhich remains adherent on the wire electrode at least in the saidregion; (c) heating means for heating the wire electrode at least in thesaid region; (d) breaking means for cutting the heated wire electrode atthe said region; and (e) means for threading the broken wire electrodefrom one broken end portion thereof through a starting hole preformed ina workpiece for machining a contour therein in the subsequent machiningoperation to reestablish the continuous stretch of the wire electrodebetween the supply and collection sides.

BRIEF DESCRIPTION OF THE DRAWING

These and other objects, features and advantages of the presentinvention will become more readily apparent from the followingdescription of certain embodiments thereof as taken with reference tothe accompanying drawing in which:

FIG. 1 is an elevational view essentially in section diagrammaticallyillustrating an automatic wire resetting apparatus incorporating theprinciples of the present invention;

FIG. 2 is a schematic view of a grooving tool embodied in the apparatusof FIG. 1 according to the present invention;

FIGS. 3(a) and 3(b) are schematic views of a wire electrode grooved andbroken according to the conventional method and apparatus; and

FIGS. 4(a) and 4(b) are schematic views of a wire electrode grooved andbroken according to the invention.

SPECIFIC DESCRIPTION

Referring now to FIG. 1, a traveling-wire electroerosion machine isshown comprising a vertical column 1 formed with an upper horizontalextension 2. A machine head 3 is slidably carried by the horizontalextension 2 and vertically displaceable by a motor 4 for adjustment ofits vertical position. A thin wire electrode E which is of a diameter,say, of 0.05 to 0.5 mm, is stored in a supply reel 5 shown mounted at anupper site in the column 1 and guided via brake rollers 6a, 6b and aguide roller 7 in the horizontal extension 2 and then via rollers 8 and9 and a die guide 10 in the head 3 towards the region of a workpiece W,which is securely mounted on a work stand or table 11. The latter iscarried on a cross-slide table arrangement 12, 13 which is in turncarried on a base 14 of the machine. The wire electrode E is positionedin a machining relationship with the workpiece W by and between the dieguide 10 located on its upper side in the head 3 and a slide guide 15located on its lower side in a hollow arm 16 which extends horizontallyfrom the vertical column 1 beneath the workpiece W. A wire drive unit 17is disposed below the slide guide 15 within the hollow arm 16 andconstituted as a pair of abutting rollers 17a and 17b one of which isdriven by a motor (not shown) to give a continuous traction to the wireelectrode E. Further shown arranged in the arm 16 is a wire pull-outsystem 18 comprising three endless belts 19, 20 and 21 wound on pairs ofrollers: 22 and 23; 24 and 25; and 23 and 26, respectively. In thisarrangement, the rollers 23 and 24 may be driven by a motor or motors(not shown) to move these belts and to seize the wire electrode E firstbetween the moving belts 19 and 20 and then between the moving belts 20and 21. The wire electrode E squeezed out from between the moving belts20 and 21 is collected in a collection box 27.

Against the traction force exerted on the wire electrode E by the driverollers 17a and 17b downstream of the workpiece W, the brake rollers 6aand 6b on the wire supply side are driven to apply an appropriatebraking force to the wire electrode E so that the latter continuouslytravels from the supply side 5 to the collection side 27 at anappropriate rate of axial travel and under an appropriate tension. Theguide roller 7 and the pull-out unit 18 serve to change the direction ofwire travel from the supply side to the workpiece W and from the latterto the collection site 27, respectively. Downstream of thedirection-changing guide roller 7, an electrically conductive roller 28is disposed in an abutting relationship with the guide roller 8 toconduct the electroerosion current to the wire electrode E and is thusconnected via a brush 29 to one output terminal of an electroerosionpower supply 30 which has the other output terminal electricallyconnected to the workpiece via a conducting block (not shown). Theelectroerosion current is thus passed through the machining gap G formedbetween the wire electrode E and the workpiece W and flushed with amachining liquid. A pump 31 draws the machining liquid from a reservoir32 to furnish it to a plenum chamber 33 attached to the head 3 tosuspend from its lower end and formed with a liquid delivery opening 34.The machining liquid pumped into the chamber 33 is delivered through theopening 34 onto the traveling wire electrode E and carried into themachining gap G therewith. A tubular electromechanical tansducer 35 maybe arranged, through which to allow the wire electrode E to pass andwhich is energized by a power supply (not shown) to impart ahigh-frequency mechanical vibration to the traveling wire electrode E tofacilitate an electroerosion process. The transducer 35 is shownsupported on an L-shaped arm 36 suspending from the outer wall of thehorizontal extension 2 and its vertical position is adjusted by aposition adjustment unit 37.

The cross tables 12 and 13 carrying the work stand 11 are driven in anX-Y plane, by means of an X-axis motor 38 and a Y-axis motor 39drivingly coupled therewith, respectively. The motors 38 and 39 areenergized with X-axis and Y-axis drive signals furnished from anumerical-control (NC) unit 40 to displace the workpiece W relative tothe axis of the wire electrode E to establish a given relativemachining-start position preprogrammed in the NC unit 40 and to displacethe workpiece W relative to the axis of the traveling wire electrode Ealong a prescribed cutting path preprogrammed in the NC unit 40.

The apparatus shown is further provided with a wire braking unit 50 anda wire heating unit 60.

The wire breaking unit 50 is shown disposed immediately beneath theworkpiece W and supported on the arm 16. As more specifically shown inFIG. 2, the unit 50 may comprise a grooving tool 51 in the form of acutting plier having a pair of legs 51a and 51b hinged at a pin 51c andcrossed thereat to extend into a pair of fingers 51d and 51e,respectively. The fingers 51d and 51e are formed with blades 51f and51g, respectively, which are opposed and normally sufficiently spacedapart by means of springs 51h and 51i bridged across the fingers 51d and51e. The blades wire pull-out unit 18 and the braking unit 6 aredeenergized to halt the axial drive of the wire electrode E and the pump31 is deactuated to discontinue the delivery of the machining liquid tothe wire electrode E. Then the cross-table unit 12, 13 may be or mayhave been driven to return the position of the axis of the wireelectrode E to the original starting hole h1. In this state, the wireelectrode E remains threaded through the hole h1 and stretchedstationarily along the machining wire drive path. A roller 91 disposedin the head 3 at the same level as the roller 9 is now moved to comeinto engagement with the latter to define a stretch of the wireelectrode E between them and the rollers 17a and 17b. For proceedingwith the wire breaking step, the heater means 60 may be actuated to heatthe stretch of the wire electrode E at least in the region of thecutting tool 51, thereby removing the internal stress and effectinghardening of the wire electrode E. At the same time, the wire brakingdrive unit 6 is driven to a predetermined extent to stretch the wireelectrode E being heated to maintain its straightened state as desired.The heating unit may be an external heater of any conventional designbut may also be a direct heating system for passing a heating currentdirectly through a stretch of the wire electrode E between, say, the dieguide 10 and the slide guide 15. The simultaneous heating and stretchingis advantageous to achieve straightening and smoothening of the wireelectrode E.

After or immediately upon deactuation of the heating unit 60 orterminating the heating current, the signal generator 55 in the wirebreaking system 50 is actuated to render the switch 54 conductive. Thecoil 52b is then energized by the power supply 53 to electromagneticallyattract the magnetic pieces 51j and 51k to the core member 52a. Thiscauses the blades 51f and 51g to come into engagement with the wireelectrode E to form the latter with a pair of coplanar grooves g1 and g2symmetrical about the axis thereof as shown in FIG. 4 (a). When thesignal ends, the coil 52b is deenergized to allow the blades 51f and 51gto return into disengagement with the wire electrode E. The wire brakingdrive unit 6 is now again actuated to give a sufficient tension to allowthe wire electrode E to be broken at the grooves g1 and g2. The brakingdrive 6 may continue to be driven by a predetermined extent to allow theupper broken end of the wire electrode E to be removed from the hole h1to a suitable position above the upper surface of the workpiece W. Atthe same time, the pull-out unit 18 is actuated to remove the lowerportion of the broken wire to the collection box 27. The work drive unit12, 13 is then actuated to displace the workpiece W to position a nextstarting hole h2 immediately below the retracted upper broken end of thewire electrode and coaxial therewith. Thereafter one of the abuttingguide rollers 9 and 90 is driven by a motor (not shown) to advance theupper broken end of the wire electrode E into, through and out of thestarting hole h2 and then through the drive rollers 17a and 17b until itcomes in contact with the belts 19 51f and 51g are designed to becoplanar and positioned, in the arrangement of FIGS. 1 and 2, so as toplace the wire electrode E between them in such a manner that the axisof the wire electrode E passes precisely perpendicular to the plane ofthe blades 51f and 51g and out of contact with these blades. The legs51a and 51b of the tool 51 are formed at their respective ends withmagnetic pieces 51j and 51k having a core member 52a of a solenoid 52bplaced therebetween. By virtue of the springs 51h and 51i, the magneticpieces 51j and 51k are normally spaced from the core member 52a. Thesolenoid coil 52b is energizable by a DC source 53 via a switch 54 shownby a transistor designed to be turned on by a signal generator 55. Whenthe switch 54 is rendered conductive in response to an automatic signalfurnished from the generator 55, the solenoid 52 is actuated toelectromagnetically attract the magnetic pieces 51j and 51k to the coremember 52b. This causes the blades 51f and g in the tool member 51 tocome into engagement with the wire electrode E to form a pair ofcoplanar grooves symmetrical about the center axis thereof as shown inFIG. 4(a) and designated at g1 and g2 therein. The grooves g1 and g2should have an appropriate depth which may be determined by the lengthof the core member 52a interposed between the magnetic pieces 51j and51k.

At the end of a given traveling-wire electroerosion machining operation,the power supply 30 is switched off to discontinue the supply of theelectroerosion current to the wire electrode E, and the drive motors forthe wire traction unit 17, the and 20. The drive unit 17 and thepull-out unit 18 are then actuated to allow the upper broken end of thewire electrode E to be squeezed and advanced by and between the movingbelts 20 and 21 and eventually to be led into the collection box 27. Theoriginal continuous stretch of the wire electrode E is thusreestablished from the supply side 5 and the collection side 27.

In the wire resetting operation, therefore, breaking of the wireelectrode to provide a straight broken end thereof is achieved withoutfail, permitting the broken end to be threaded into and through a newstarting hole without fail.

The apparatus of FIG. 1 also includes an air jet nozzle 70 ahownsupported on an L-shaped arm 71 suspending from the outer wall of thehorizontal extension 2 and provided with a position adjustment unit 72to adjust its vertical position. The nozzle 70 is fed with a pressurizedgas, e.g. air, from a compressor or any other pressurized gas supply 73via a conduit 74 to apply a stream of the pressurized gas or air to theregion of the previous starting hole h1 and the previously machinedcontour in the workpiece W and to the portion of the wire electrode Etherein and the portion of the wire electrode E in the region therebelowto be heated with the heater 60 and grooved by the grooving tool 51 andbroken. By virtue of the pressurized gas or air applied to theseregions, any residue to the machining liquid that may remain adherent onthe wire electrode E in the heating region is blown off and the wireelectrode E is allowed to be uniformly heated practically withoutcausing any localized thermal stress. This allows the wire electrode Ein the resetting operation to be broken to provide a straight broken endthereof without fail, permitting the broken end to be threaded into andthrough a new starting hole without fail.

What is claimed is:
 1. An apparatus for automatically resetting a wireelectrode in an operating setup on an electroerosion machine includingan electroerosion power supply for applying a machining electric currentto the wire electrode, wire drive means for axially advancing the wireelectrode extending in a continuous stretch from a supply side to acollection side and liquid supply means for furnishing a machiningliquid to the wire electrode and a machining gap formed thereby with aworkpiece, the apparatus comprising: (a) switch means associated withthe power supply and the wire drive means for shutting off the supply ofsaid machining electric current to said wire electrode and halting amachining axial advance of said wire electrode in said continuousstretch, thereby terminating a previous machining operation commencedwith a given starting hole; (b) wire breaking means comprising (b1)grooving cutter means having at least two blade means disposed in aregion adjacent to the workpiece and at one of the opposite sidesthereof for forming said wire electrode in said region with at least twocoplanar grooves substantially symmetrical about the center axis thereofand (b2) tension means for applying a tension to said wire electrode tobreak the latter at said grooves; (c) means for threading said wireelectrode from one broken end portion thereof through a next startinghole preformed in a workpiece for machining a contour therein in thesubsequent machining operation to reestablish the continuous stretch ofsaid wire electrode between said supply side and said collection sideand means for heating, prior to breaking, said wire electrode at leastalong said region to effect a hardening thereof.
 2. A method ofautomatically resetting a wire electrode in an operating setup on atraveling-wire electroerosion machine, comprising the steps of:(a)terminating a previous machining operation performed with the sametraveling-wire electroerosion machine by shutting off supply of amachining electrical current to a said wire electrode, halting an axialadvance of the latter electrode extending in a continuous stretch from asupply side to a collection side along a straight path passing through aworkpiece and discontinuing delivery of a machining liquid to said wireelectrode at said workpiece; (b) subsequent to step (a), heating saidwire electrode at least along a region thereof adjacent to saidworkpiece and located at one of the opposite sides thereof to removeinternal stress of the wire electrode in said region; (c) subsequent tostep (b), breaking said wire electrode in said region by forming in saidheated region of the halted wire electrode at least two coplaner groovesdisposed substantially symmetrically about the longitudinal axis thereofand then applying a tension to said wire electrode to allow the latterto be severed at a neck formed by said grooves in said region; and (d)thereafter, threading one broken end portion of said severed wireelectrode through a workpiece for machining a contour therein in asubsequent machining operation to reestablish a said continuous stretchof the wire electrode between said supply side and said collection side.3. A method of automatically resetting a wire electrode in an operatingsetup on a traveling-wire electroerosion machine, comprising the stepsof:(a) terminating a previous machining operation performed with thesame traveling-wire electroerosion machine by shutting off supply of amachining electrical current to a said wire electrode, halting an axialadvance of the latter electrode extending in a continuous stretch from asupply side to a collection side along a straight path passing through aworkpiece and discontinuing delivery of a machining liquid to said wireelectrode at said workpiece; (b) breaking said halted wire electrode ata region thereof adjacent to said workpiece and located at one of theopposite sides of the workpiece by heating said halted wire electrode atleast along said region of the wire electrode to remove internal stressof the wire electrode in said region, forming in said heated region ofthe wire electrode at least two coplanar grooves disposed substantiallysymmetrically about the longitudinal axis thereof and then applying atension to said wire electrode to allow the latter to be severed at aneck formed by said grooves in said region; and (c) thereafter,threading one broken end portion of said severed wire electrode througha workpiece for machining a contour therein in a subsequent machiningoperation to reestablish a said continuous stretch of the wire electrodebetween said supply side and said collection side.
 4. An apparatus forautomatically resetting a wire electrode in an operating setup on atraveling-wire electroerosion machine which includes an electroerosionpower supply for applying a machining electric current to the wireelectrode, wire drive means for axially advancing the wire electrodeextending in a continuous stretch form a supply side to a collectionside, and liquid supply means for furnishing a machining liquid to thewire electrode and a machining gap formed thereby with a workpiece, theapparatus comprising:(a) switch means associated with the power supplyand the wire drive means for shutting off the supply of said machiningelectric current to said wire electrode, halting a machining axialadvance of said wire electrode in said continuous stretch anddiscontinuing a furnishment of said machining liquid to the wireelectrode, thereby terminating a previous machining operation commencedwith a given starting position and performed with said machine; (b)means for heating, subsequent to terminating the previous machiningoperation by said switch means, said wire electrode at least along aregion thereof adjacent to the workpiece and at one of the oppositesides of the workpiece to remove internal stress of said wire electrodein said region; (c) wire breaking means comprising:(c1) grooving meanshaving at least two blade members disposed proximate to said region forforming in said heated region of the wire electrode at least twocoplanar grooves disposed substantially symmetrically about thelongitudinal axis thereof and (c2) tension means for applying a tensionto said wire electrode to sever the latter at a neck formed by saidgrooves; and (d) means for threading one broken end portion of thesevered wire electrode through a workpiece for machining a contourtherein in a subsequent machining operation so as to reestablish a saidcontinuous stretch of said wire electrode between said supply side andsaid collection side.
 5. An apparatus for automatically resetting a wireelectrode in an operating setup on a traveling-wire electroerosionmachine which includes an electroerosion power supply for applying amachining electric current to the wire electrode, wire drive means foraxially advancing the wire electrode extending in a continuous stretchfrom a supply side to a collection side, and liquid supply means forfurnishing a machining liquid to the wire electrode and a machining gapformed thereby with a workpiece, the apparatus comprising;(a) switchmeans associated with the power supply and the wire drive means forshutting off the supply of said machining electric current to said wireelectrode, halting a machining axial advance of said wire electrode insaid continuous stretch and discontinuing a furnishment of saidmachining liquid to the wire electrode, thereby terminating a previousmachining operation commenced with a given starting position andperformed with said machine; (b) wire breaking means comprising:(b1)means for heating, subsequent to terminating the previous machiningoperation by said switch means and prior to breaking, said wireelectrode at least along a region thereof adjacent to the workpiece andat one of the opposite sides thereof to remove internal stress of saidwire electrode in said region, (b2) grooving means having at least twoblade members disposed proximate to said region for forming in saidheated region of the wire electrode at least two coplanar groovesdisposed substantially symmetrically about the longitudinal axisthereof, and (b3) tension means for applying a tension to said wireelectrode to sever the latter at a neck formed by said grooves; and (e)means for threading one broken end portion of the severed wire electrodethrough a workpiece for machining a contour therein in a subsequentmachining operation so as to reestablish a said continuous stretch ofsaid wire electrode between said supply side and said collection side.